Side Illumination Scanning Interferometry High-Slope Surfaces
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Solution Overview
Problem
Conventional scanning interferometers face challenges in measuring surfaces with high slopes and roughness due to fringe deficiencies, requiring complex data processing and precise sample manipulation, and non-interferometric methods are less accurate for smooth surfaces.
Innovation Solution
Combining side illumination with scanning interferometry, using multiple light sources around the interferometric objective to provide additional irradiance, allowing for simultaneous interferometric and depth-from-focus data processing, enabling complete profilometric measurement of surfaces with high slopes and roughness in a single scan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional scanning interferometry is used to measure smooth surfaces with low slopes, then measurement precision is improved, but the system cannot measure high-slope or rough surfaces due to fringe deficiencies
Solution Approach 1:
The patent combines scanning interferometry and contrast-based depth-from-focus methods into a single hybrid system. The interferometric objective and detector are used for both interferometric fringe detection and conventional imaging, allowing the system to automatically select or combine measurement modes based on surface characteristics, thus resolving the contradiction between measurement precision for smooth surfaces and adaptability for rough/high-slope surfaces
Solution Approach 2:
The interferometric objective is made multi-functional by using it for both interferometric measurements (with coherent light) and conventional contrast-based imaging (with incoherent or partially coherent light). This universal objective design allows the single instrument to handle both smooth low-slope surfaces (via interferometry) and rough/high-slope surfaces (via contrast methods), eliminating the need for separate measurement systems
2Adaptability or versatility
If multiple-level illumination capability is added to increase irradiance for high-slope measurements, then the ability to measure high-slope surfaces is improved, but detector saturation occurs at higher intensity modes
Solution Approach 1:
The patent changes the illumination parameters by introducing side illumination at specific angles rather than direct normal illumination. This parameter change increases the irradiance on high-slope surfaces by directing light from the side, allowing the light to reflect off steep surfaces back toward the objective without causing detector saturation that would occur with direct high-intensity illumination
3Loss of information
If sample rotation is used to ensure sufficient light return for fringe production, then measurement completeness is improved, but device complexity and data processing complexity increase
Solution Approach 1:
The patent extracts the need for mechanical sample manipulation by implementing side illumination that can capture light from high-slope surfaces in their original orientations. The side illumination geometry allows light to reflect off steep surfaces back to the objective without requiring the sample to be rotated, thereby extracting the problematic mechanical rotation and complex stitching operations from the measurement process
4Measurement precision
If smaller objective aperture is used for interferometric profilometry, then interferometric measurement capability is maintained, but irradiance to the sample is reduced
Solution Approach 1:
The patent addresses the irradiance limitation by adding illumination from a different spatial dimension - side illumination from the sides of the objective rather than from above. This dimensional change in illumination geometry allows the small interferometric objective aperture to maintain its interferometric capability while receiving additional light from lateral directions, thereby increasing total irradiance without compromising interferometric performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies focus finding and identifies regions of interest, providing more accurate and complete surface measurements by enhancing contrast and visibility, facilitating the measurement of surfaces with high slopes and roughness without interfering with interferometric beams.
Implementation Method 1
Side illumination is sometimes added to such conventional (non-interferometric) objectives to increase irradiance to the sample
Implementation Method 2
combining side illumination with scanning interferometry, using multiple light sources around the interferometric objective
Implementation Method 3
Interferometric techniques for surface profilometry (such as vertical-scanning and phase-shift interferometric methods)
Data Source
AI summary
Side illumination is combined with scanning interferometry to provide a means for measuring with a single data-acquisition scan surfaces that contain sections suitable for interferometric processing as well as sections that are not suitable because of lack of fringes produced by the measurement. In the sections where no fringes are produced, the irradiance detected during the scan is processed using a depth-from-focus mapping method to yield a corresponding measurement. The result is a complete profilometric measurement of the sample surface with a single scan. In addition, by increasing sample irradiance through side illumination, the structural features of the sample become markedly more visible than when illuminated only by the object beam of the interferometer, which greatly facilitates finding focus and identifying regions of interest for the measurement.